N-hydroxypipecolic acid is a general activator of systemic immunity in plants.
Due to their expertise in plant immunity, IPB’s Tina Romeis and Tiziana Guerra from the Leibniz Institute of Vegetable and Ornamental Crops recently wrote a commentary for the Journal of Experimental Botany. In their article, the authors discuss a study by Anika Schnake et al. on the role of N-hydroxypipecolic acid (NHP) in Systemic Acquired Resistance (SAR) of plants. N-hydroxypipecolic acid turns out to be the long searched key molecule in this immune-related signaling scenario. Induced by pathogen infestation, it accumulates in the distal leaves 24 hours after local infection and is essential for the activation of SAR. Also its precursor molecule, pipecolinic acid (Pip), exhibits immunoregulatory properties. However, the biochemical quantification of Pip and NHP metabolite levels during infection has been a major challenge so far and therefore hardly succeeded. Schnake et al. have now closed this gap.
Using six different phytopathosystems, consisting of dicotyledonous and monocotyledonous plant species and their associated pathogens, Schnake et al. were able to quantify the absolute metabolite concentrations of NHP, Pip and the SAR-related phytohormone salicylic acid over time of the infections. While basal NHP levels in non-infected plants were low to undetectable, they increased two to ten times through pathogen infection. Also external application of NHP to cucumber, tobacco and barley leaves triggered acquired resistance in these plants. Subsequent infections with the respective plant-specific pathogens showed fewer disease symptoms. In their study, Schnake et al. document an overall presence of the NHP signaling pathway and cement its role as a general, conserved activator of plant systemic immune response. Romeis and Guerra not only consider Schnake’s results in a broader context of knowledge in this field, but also give a critical outlook with further questions.
Reference:
T. Guerra & T. Romeis. N-hydroxypipecolic acid: a general and conserved activator of systemic plant immunity. Journal of Experimental Botany 71 (20), 6193–6196, https://doi.org/10.1093/jxb/eraa345